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For most specimens submitted to the laboratory, optical crystallography is sufficient to identify the crystalline mineral components of the calculi. In addition to optical crystallography, infrared spectroscopy (IR) is routinely utilized to examine all specimens suspected of containing amorphous silica, uric acid and/or its salts, xanthine, hypoxanthine, allopurinol, or oxypurinol (a metabolite of allopurinol) that may be present in the specimens, and these additional methodologies are performed at no extra charge. Polarized light microscopy using the oil immersion method of optical crystallography alone is insufficient to distinguish xanthine, hypoxanthine, allopurinol and its metabolites, and salts of uric acid so this additional methodology is utilized.
X-ray diffractometry (XRD) is another methodology that can be utilized when polarized light microscopy is insufficient to identify the crystalline components present in a calculus. Because each crystalline structure is unique, an XRD pattern unique to the structure of crystals present in the specimen is obtained. This pattern can then be compared with the known XRD patterns of minerals catalogued by the International Centre for Diffraction Data (ICDD) to determine if a match for the crystalline component(s) can be found. Currently we routinely use XRD in conjunction with IR to identify uric acid or its salts which are present in urate calculi.
When a definitive identification of the crystalline components present in a calculus is not obtained utilizing the oil immersion method of optical crystallography, IR, and/or XRD, energy-dispersive X-ray spectroscopy can be performed to obtain an X-ray spectrum emitted by hitting the surface of the specimen by an electron beam. , The elements present in the specimen can be identified by the peaks present in the spectrum.